Method for manufacturing oxide thin film transistor

ABSTRACT

A method for manufacturing an oxide thin film transistor with leakage currents less than 10 −14  angstrom includes the steps of forming an oxide semiconductor active layer by a deposition process. In the deposition process, an electric power is in a range from 1.5 kilowatts to 10 kilowatts. The oxide thin film transistor manufactured by the above methods has advantages of low leakage currents, high electron mobility, and excellent temperature stability. The present invention also provides a method for manufacturing a display device. The display quality of the display device can be improved.

This application is a continuation application of an application Ser.No. 12/699,063, filed on Feb. 3, 2010, and the entire contents of whichare incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a method for manufacturing a thin filmtransistor, and more particularly to a method for manufacturing an oxidethin film transistor.

2. Description of the Related Art

In these days, thin film transistor display devices, such as liquidcrystal display devices, electrophoretic display devices and organiclight emitting diode display devices, have been used more and morewidely. To improve display quality of the display devices, people havealways paid attention to research and development of structure andmanufacturing method of a thin film transistor (TFT) that is one of corestructure of the display device.

A conventional thin film transistor has an active layer made ofamorphous silicon (a-Si). However, the conventional thin film transistorhas some shortcomings, such as high leakage currents, low electronmobility and some of functions of integrated circuit incapable offorming on a substrate directly. Therefore, the conventional thin filmtransistor fails to satisfy the needs of high display quality of thedisplay devices. For solving the above problems, low temperaturepolysilicon (LTPS) can be used to make the active layer. However, theprocess of making the low temperature polysilicon is complicated and hasa low product yield, thus the low temperature polysilicon is still noteasily to be used widely. Recently, an oxide thin film transistorappears, which has an active layer made of an oxide semiconductor, andcan overcomes the above mentioned problems.

However, it is a new application that the oxide semiconductor is usedfor the active layer of the oxide thin film transistor. Therefore, sometopics, such as, how to manufacture the oxide thin film transistor withgood performances, are still in research stages.

What is needed, therefore, is a new method for manufacturing an oxidethin film transistor and a new method for manufacturing a display devicethat can overcome the above-mentioned shortcomings.

BRIEF SUMMARY

The present invention relates to a method for manufacturing an oxidethin film transistor, where the oxide thin film transistor hasadvantages of low leakage currents, high electron mobility and excellenttemperature stability.

To achieve the above-mentioned advantage, the present invention providesa method for manufacturing an oxide thin film transistor with leakagecurrents less than 10⁻¹⁴ angstrom. The method includes the steps offorming an oxide semiconductor active layer by a deposition process. Inthe deposition process, a gas used includes oxygen with a flow ratio tothe total gas in a range from 4% to 20%.

To achieve the above-mentioned advantage, the present invention providesa method for manufacturing an oxide thin film transistor with leakagecurrents less than 10⁻¹⁴ angstrom. The method includes the steps offorming an oxide semiconductor active layer with a thickness in a rangefrom 300 angstroms to 2000 angstroms by a deposition process.

To achieve the above-mentioned advantage, the present invention providesa method for manufacturing an oxide thin film transistor with leakagecurrents less than 10⁻¹⁴ angstrom. The method includes the steps offorming an oxide semiconductor active layer by a deposition process. Inthe deposition process, an electric power is in a range from 1.5kilowatts to 10 kilowatts.

In one embodiment, the deposition process is a sputtering depositionprocess. In one embodiment, material of the oxide semiconductor activelayer is selected from the group consisting of zinc oxide, zinc tinoxide, chromium zinc oxide, gallium zinc oxide, titanium zinc oxide,indium gallium zinc oxide, copper aluminum oxide, strontium copperoxide, lanthanum copper oxide and any combination thereof.

In the method for manufacturing the oxide thin film transistor of thepresent invention, the oxide semiconductor active layer is formed by thedeposition process. In the deposition process, an electric power is inthe range from 1.5 kilowatts to 10 kilowatts, so that suitable plasmacan be produced to deposit an oxide semiconductor. The oxide thin filmtransistor that is manufactured by the above methods has advantages oflow leakage currents, high electron mobility, and excellent temperaturestability. And thus, if the oxide thin film transistor is used in thedisplay device, the display device can have an improved display quality.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is a schematic, side cross-sectional view of a display deviceaccording to a first embodiment of the present invention.

FIG. 2 is a flow chart of the method for manufacturing the displaydevice of FIG. 1.

FIG. 3 is a curve graph of drain current and gate voltage of an oxidethin film transistor according to the present invention.

FIG. 4 is a schematic, side cross-sectional view of a display deviceaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION

A display device includes a plurality of pixels. Structures of thepixels are substantially the same with each other; therefore, only onepixel would be shown illustratively to present the all pixels of thedisplay device in the following drawings.

FIG. 1 is a schematic, side cross-sectional view of a display deviceaccording to a first embodiment of the present invention. Referring toFIG. 1, the display device 100 can be, but not limited to, anelectrophoretic display device. In this embodiment, the display device100 includes a substrate 110, an oxide thin film transistor array (notlabeled) formed on the substrate 110 and a display layer 130 disposed onthe oxide thin film transistor array. The oxide thin film transistorarray can include a plurality of oxide thin film transistors 120, andonly one of the oxide thin film transistors 120 is shown illustrativelyin FIG. 1.

A method for manufacturing the display device 100 would be describeddetailedly below. It should be noted that, the following description ofthe method for manufacturing the display device 100 is not limitation.For example, the various steps in the method may be arranged in adifferent sequence to achieve a similar effect.

FIG. 2 is a flow chart of the method for manufacturing the displaydevice 100 of FIG. 1. Referring to FIG. 2, firstly, at step 10, asubstrate 110 is provided. The substrate 110 can be a transparent glasssubstrate or an acrylic substrate. In this embodiment, a surface of thesubstrate 110 is mainly used to form an oxide thin film transistor arraythereon.

At steps 11 to 14, the oxide thin film transistor array is formed on thesurface of the substrate 110. In detail, at step 11, a gate 121 isformed on the surface of the substrate 110. At step 12, a gateinsulating layer 122 is formed on the gate 121, so as to cover the gate121. At step 13, an oxide semiconductor active layer 123 is formed onthe gate insulating layer 122 by a deposition process. At step 14, asource 124 and a drain 125 are formed on the gate insulating layer 122,and the source 124 and the drain 125 are electrically connected with theoxide semiconductor active layer 123 respectively. As such, the oxidethin film transistor 120 is made. Material of the oxide semiconductoractive layer 123 can be selected from the group consisting of zinc oxide(ZnO), zinc tin oxide (ZnSnO), chromium zinc oxide (CrSnO), gallium zincoxide (GaSnO), titanium zinc oxide (TiSnO), indium gallium zinc oxide(InGaZnO , IGZO), copper aluminum oxide (CuAlO), strontium copper oxide(SrCuO), lanthanum copper oxide (LaCuOS) and any suitable combinationthereof. In this embodiment, the oxide semiconductor active layer 123 ismade of indium gallium zinc oxide, and the following process ofmanufacturing the oxide semiconductor active layer 123 is described bytaking indium gallium zinc oxide as an example.

In detail, when the oxide semiconductor active layer 123 is formed bythe deposition process, a total flow rate of a gas can be more than 100standard cubic centimeters per minute (sccm) and an electric power canbe in a range from 1.5 kilowatts to 10 kilowatts, so that suitableplasma can be produced to deposit an oxide semiconductor. The gas caninclude oxygen (O₂) and argon (Ar). A flow ratio of oxygen to the totalgas can be in a range from 4% to 20%. A thickness of the oxidesemiconductor active layer 123 can be in a range from 300 angstroms to2000 angstroms. In this embodiment, the oxide semiconductor active layer123 can be, but not limited to, formed by a sputtering depositionprocess.

Referring to FIG. 2, after the source 124 and the drain 125 is formed,at step 15, a protection film 126 and a resin layer 127 can be formed onthe source 124 and the drain 125, and a pixel electrode 128 can beformed to electrically connect to the drain 125.

In this embodiment, the oxide thin film transistor 120 is a bottom gatetype. In an alternative embodiment, the oxide thin film transistor 120can be a top gate type. Relative to the top bottom gate type, when theoxide thin film transistor 120 is the top gate type, an order of formingthe various electrodes has a little difference, but the process offorming the oxide semiconductor active layer 123 is the same.

Referring to FIG. 2, at steps 16, a display layer 130 is disposed on theoxide thin film transistor array. In this embodiment, the display layer130 is an electrophoretic display layer. The electrophoretic displaylayer can be a microcapsule electrophoretic display layer or a microcupelectrophoretic display layer. In addition, a color filter (not shown)can further be disposed on the display layer 130, so that the displaydevice 100 may achieve color display. It should be understood that, themethod for manufacturing the display device 100 may further includingdisposing a protecting layer 140 to seal the display device 100,configuring an integrated circuit, and connecting to a printed circuitboard (not shown).

In this embodiment, the oxide semiconductor active layer 123 of theoxide thin film transistor 120 is formed by the deposition process. Bycontrolling the conditions of deposition process, the oxide thin filmtransistor 120 with good performances can be obtained easily. FIG. 3 isa curve graph of drain current and gate voltage (Id-Vg) of the oxidethin film transistor 120, wherein, the drain voltages (Vd) are 0.1 volt(V), 9.9V and 5V respectively. The performances of the oxide thin filmtransistor 120 manufactured by the above methods can keep stability,after being heated at 200 Celsius degree for two hours. In other words,the reliability of the oxide thin film transistor 120 can not beinfluenced easily by temperature, and the oxide thin film transistor 120has excellent temperature stability. In addition, leakage currents ofthe oxide thin film transistor 120 can be less than 10⁻¹⁴, and even ifthe oxide thin film transistor 120 is under sunlight or ultravioletradiation, the leakage currents would still not increase. Electronmobility of the oxide thin film transistor 120 can be 2 squarecentimeters per volt per second (cm²/V sec). Therefore, the oxide thinfilm transistor 120 has advantages of low leakage currents, highelectron mobility, and excellent temperature stability. And thus, whenthe oxide thin film transistor 120 is used in the display device 100,the display device 100 can have an improved display quality.

FIG. 4 is a schematic, side cross-sectional view of a display deviceaccording to a second embodiment of the present invention. Referring toFIG. 4, the display device 100 a can be, but not limited to, a liquidcrystal display device. In this embodiment, the method for manufacturingthe display device 100 a is similar to that of the method formanufacturing the display device 100 of the first embodiment. Thedifference is that an oxide thin film transistor 120 a is a top gatetype. A process of forming an oxide semiconductor active layer 123 a canbe the same to that of the oxide semiconductor active layer 123 of theoxide thin film transistor 120, but the order of forming the variouslayers in the oxide thin film transistor 120 a has a little difference.

In detail, the oxide thin film transistor 120 a is formed by thefollowing steps. Firstly, a source 124 a and a drain 125 a are formed ona surface of the substrate 110 a. Secondly, an oxide semiconductoractive layer 123 a is formed on the surface of the substrate 110 a by adeposition process, and the oxide semiconductor active layer 123 a iselectrically connected with the source 124 a and the drain 125 arespectively. Thirdly, a gate insulating layer 122 a is formed on thesource 124 a, the drain 125 a and the oxide semiconductor active layer123 a, so as to cover the source 124 a, the drain 125 a and the oxidesemiconductor active layer 123 a. Fourthly, a gate 121 a is formed onthe gate insulating layer 122 a, and corresponds to the oxidesemiconductor active layer 123 a. Fifthly, an insulation protection film126 a is formed on the gate 121 a. As such, the oxide thin filmtransistor 120 a is made.

It should be understood that, for manufacturing the display device 100a, a pixel electrode 128 a should be formed to electrically connect tothe drain 125 a, and some other layers may be configured according tothe requirement of the display device 100 a. In particular, a displaylayer 130 a of the display device 100 a is a liquid crystal displaylayer, and a cell gap of the liquid crystal display layer can be in arange from 3 micrometers to 6 micrometers. Furthermore, a color filtersubstrate that includes an alignment film 150, a common electrode 160, acolor filter layer 170, an insulation protection film 126 a and an uppersubstrate 180 formed on the display layer 130 a in the above mentionedorder, is configured so as to make the display device 100 a achievedisplay. In addition, for manufacturing the display device 100 a, stepsof configuring an integrated circuit (not shown) and connecting with theprinted circuit board (not shown) may also be required.

It should be noted that, the display layer of the display device can beother display layers, such as an organic light emitting diode displaylayer. When the display layer is the organic light emitting diodedisplay layer, the oxide thin film transistor can be a bottom gate typeor a top gate type, and the method for manufacturing the display deviceshould be modified properly. The organic light emitting diode displaylayer can be bottom-emitting or top-emitting.

In summary, in the method for manufacturing the oxide thin filmtransistor and the method for manufacturing the display device of thepresent invention, the oxide semiconductor active layer is formed by thedeposition process. In the deposition process, a total flow rate of agas is more than 100 standard cubic centimeters per minute and anelectric power is in the range from 1.5 kilowatts to 10 kilowatts, sothat suitable plasma can be produced to deposit an oxide semiconductor.The oxide thin film transistor that is manufactured by the above methodshas low leakage currents, high electron mobility, and excellenttemperature stability. And thus, when the oxide thin film transistor isused in the display device, the display device can have an improveddisplay quality.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein, including configurations ways of the recessed portionsand materials and/or designs of the attaching structures. Further, thevarious features of the embodiments disclosed herein can be used alone,or in varying combinations with each other and are not intended to belimited to the specific combination described herein. Thus, the scope ofthe claims is not to be limited by the illustrated embodiments.

What is claimed is:
 1. A method for manufacturing an oxide thin filmtransistor with leakage currents less than 10⁻¹⁴ angstrom, comprising:forming an oxide semiconductor active layer by a deposition process,wherein a gas used in the deposition process comprises oxygen with aflow ratio to the total gas in a range from 4% to 20%.
 2. The method formanufacturing an oxide thin film transistor as claimed in claim 1,wherein the deposition process is a sputtering deposition process. 3.The method for manufacturing an oxide thin film transistor as claimed inclaim 1, wherein material of the oxide semiconductor active layer isselected from the group consisting of zinc oxide, zinc tin oxide,chromium zinc oxide, gallium zinc oxide, titanium zinc oxide, indiumgallium zinc oxide, copper aluminum oxide, strontium copper oxide,lanthanum copper oxide and any combination thereof.
 4. The method formanufacturing an oxide thin film transistor as claimed in claim 1,wherein a thickness of the oxide semiconductor active layer is in arange from 300 angstroms to 2000 angstroms.
 5. The method formanufacturing an oxide thin film transistor as claimed in claim 1,wherein the gas used in the deposition process further comprises argon.6. The method for manufacturing an oxide thin film transistor as claimedin claim 1, wherein an electric power used in the deposition process isin range from 1.5 kilowatts to 10 kilowatts.
 7. A method formanufacturing an oxide thin film transistor with leakage currents lessthan 10⁻¹⁴ angstrom, comprising: forming an oxide semiconductor activelayer with a thickness in a range from 300 angstroms to 2000 angstromsby a deposition process.
 8. The method for manufacturing an oxide thinfilm transistor as claimed in claim 6, wherein the deposition process isa sputtering deposition process.
 9. The method for manufacturing anoxide thin film transistor as claimed in claim 6, wherein material ofthe oxide semiconductor active layer is selected from the groupconsisting of zinc oxide, zinc tin oxide, chromium zinc oxide, galliumzinc oxide, titanium zinc oxide, indium gallium zinc oxide, copperaluminum oxide, strontium copper oxide, lanthanum copper oxide and anycombination thereof.
 10. The method for manufacturing an oxide thin filmtransistor as claimed in claim 6, wherein an electric power used in thedeposition process is in range from 1.5 kilowatts to 10 kilowatts.
 11. Amethod for manufacturing an oxide thin film transistor with leakagecurrents less than 10⁻¹⁴ angstrom, comprising: forming an oxidesemiconductor active layer by a deposition process, wherein an electricpower used in the deposition process is in range from 1.5 kilowatts to10 kilowatts.
 12. The method for manufacturing an oxide thin filmtransistor as claimed in claim 11, wherein the deposition process is asputtering deposition process.
 13. The method for manufacturing an oxidethin film transistor as claimed in claim 11, wherein material of theoxide semiconductor active layer is selected from the group consistingof zinc oxide, zinc tin oxide, chromium zinc oxide, gallium zinc oxide,titanium zinc oxide, indium gallium zinc oxide, copper aluminum oxide,strontium copper oxide, lanthanum copper oxide and any combinationthereof.